This invention relates to a hydrodynamic bearing comprising at least one bearing shoe with a lower part and an upper part tiltably and rotatably supported thereon and further comprising a starting aid in the form of a device designed to be switched on and off for producing a hydrostatic pressure in the bearing gap.
In contrast to hydrostatic plain bearings, to which the pressure medium has to be supplied under certain minimum pressure, the pressure medium required for producing a hydrodynamic pressure in the bearing gap in the case of a hydrodynamic plain bearing may be delivered to the bearing surface in the absence of pressure or in the substantial absence of pressure, because by virtue of the geometry of the upper part of the bearing shoe the hydrodynamic pressure is built up by a wedge-shaped layer of pressure medium.
One major disadvantage of known hydrodynamic bearings is that, in many cases, only a relatively thin layer of pressure medium or lubricant can be built up in operation between the bearing surface and the rotating element to be supported, i.e., in the bearing gap, which can have an unfavorable effect, particularly during the startup of the rotating element to be supported and, in some cases, also with relatively slowly rotating, large machine parts. Attempts have been made to obviate these disadvantages by associating with hydrodynamic bearings additional devices which are intended in particular to serve as starting aids and which are designed to be switched on and off during the startup phase to produce a hydrostatic pressure in the bearing gap. In this connection, it is known that the switching-on and switching-off of the starting aid may be controlled through a temperature monitor. However, a control arrangement such as this has proved to be problematical in practice on account of its relatively high inertia (time delay).